This invention relates generally to systems for controlling with greatly improved accuracy the motion of servo systems, numerically controlled systems, and any other system which produces controlled motion in response to a control signal, and more particularly, to a system which provides control signal compensation for forces which disturb the motion of the system, such as friction forces, whereby the resulting motion corresponds accurately to the desired motion.
The tracking ability of moving slides or rotating shafts to position or velocity commands deteriorates because of the friction forces in the guideways, leadscrews, gears, and other resistance forces caused by the slide assembly. When the combined motion of two slides (x, y) that are not parallel (e.g., perpendicular) is needed, the tracking deficiency causes a position error in the resultant trajectory, as shown in FIG. 1. In machining, this position error along the part contour is called the contour error. One of the reasons that a part cannot be machined on a milling machine precisely to a desired contour is that the friction in the guideways in the x, y and z axes of motion disturbs, or counteracts, the intended motion of the machine tool, ultimately resulting in contour errors.
Milling machines are not the only systems which are subject to loss of accuracy due to the effects of friction and other forces which disturb the motion. Other products that may benefit from a system which compensates for such disturbances include machine tools, robots, welders, laser-beam cutters and welders, water-jet cutters, medical scanners, weapon tracking systems (missile launchers, anti-aircraft cannons, tanks, etc.), and any other system requiring a motion of one slide or shaft, or a combined motion of several axes, for its operation. An additional family of products where compensation for repeatable disturbances is useful includes optical measurement and inspection systems of the type which use moving members as part of the measurement system.
It is, therefore, an object of this invention to provide a simple and economical system for controlling the motion of a servo system so that it travels accurately and precisely along a desired predetermined path;
It is another object of this invention to provide a system which reduces position errors and contour errors in a numerically controlled system.
It is a further object of this invention to provide a system which compensates for the effects of undesirable forces which disturb the motion of a numerically controlled system.
It is also an object of this invention to improve the trackability of a moving slide or a rotating shaft by compensating for stiction.
It is additionally an object of this invention to improve the tracking ability of moving slides and rotating shafts to velocity or position commands.
It is yet a further object of this invention to improve the position precision of systems that combine motion of two or more moving slides or shafts by compensating for the friction of the guideways, leadscrews, gears, and other moving members.
It is also another object of this invention to reduce position tracking error resulting from friction.
It is yet an additional object of this invention to provide a system which reduces errors resulting from repeatable disturbances, such as friction.
It is still another object of this invention to provide a system which reduces errors in controlled cyclical motion resulting from repeatable disturbances, such as friction.
It is yet another object of the invention to provide a system which reduces errors resulting from stiction.